A recent review article used the term intradural/intramedullary IVD extrusion (IIVDE) to collectively describe these cases, including both cases with and without features of nucleus pulposus degeneration in that classification (88). It is possible that more advanced systems of characterizing IVD degeneration, in combination with advances in genetic investigations, clinical understanding and diagnostic imaging techniques, will allow a more accurate and uniform system of classifying disease of the IVD in the future. Olsson SE. De Risio L. A review of fibrocartilaginous embolic myelopathy and different types of peracute non-compressive intervertebral disk extrusions in dogs and cats. Borlace T, Gutierrez-Quintana R, Taylor-Brown FE, De Decker S. Comparison of medical and surgical treatment for acute cervical compressive hydrated nucleus pulposus extrusion in dogs. (2014) 55:1829. J Am Vet Med Assoc. (2015) 56:1607. Spine. Acute change in neurological level following canine intervertebral disc herniation. (2007) 160:7959. Davies JV, Sharp NJH. As a result of the similarities in presentation of dogs with IIVDE and either Hansen Type I IVD extrusion, traumatic IVD extusion or ANNPE, antemortem diagnosis is dependent on accurate interpretation of diagnostic imaging, or surgical confirmation of intradural or intramedullary disc material. Dogs therefore most often present with an acute onset of tetraparesis or tetraplegia, with symmetrical clinical signs more common in contrast to the lateralisation seen with ANNPE (20). (2013) 195:15663. How long and low can you go? On CT imaging the hemorrhage/hematoma is identified as a moderately hyperattenuating [7090 Hounsfield units [HU]] extradural mass extending over multiple vertebral levels and lying dorsal, ventral and lateral to the spinal cord. (2019) 10:435. doi: 10.3390/genes10060435, 16. Ingram EA, Kale DC, Balfour RJ. Thoracolumbar intervertebral disk disease in large, nonchondrodystrophic dogs: a retrospective study. At the same time as the nuclear degeneration, it has been postulated that small separations develop in the lamellae of the annulus fibrosus, potentially exacerbated by repeated minor trauma, allowing this degenerative fibroid nuclear material to extend into and between the fibers of the annulus (5, 9, 110). Association of clinical and magnetic resonance imaging findings with outcome in dogs with presumptive acute noncompressive nucleus pulposus extrusion: 42 cases (2000-2007). (2008) 22:95460. (2014) 43:43746. doi: 10.1080/01652176.2000.9695046, 156. 148. Fardon DF, Williams AL, Dohring EJ, Murtagh FR, Gabriel Rothman SL, Sze GK. J Small Anim Pract. (1990) 15:4115. In most cases the acute onset seen in HNPE appears to occur spontaneously, without inciting causes such as intense exercise or trauma, further differentiating the clinical presentation from that of ANNPE. Other unsubstantiated theories for such cases include persistence of embryonal vasculature within the annulus fibrosus and presence of anomalous vessels or arteriovenous fistulae down which fibrocartilage can be embolized (95). The improved diagnostic ability provided by these developments has led to the increasingly frequent diagnosis of IVD conditions that occur with minimal evidence of traditional features of disc degeneration, including the herniation of relatively well-hydrated nucleus pulposus material (1820). Part Two: degenerative changesnonchondrodystrophoid versus chondrodystrophoid disks. J Small Anim Pract. J Feline Med Surg. (2010) 72:34952. Brown EA, Dickinson PJ, Mansour T, Sturges BK, Aguilar M, Young AE, et al. Incidence of contralateral versus ipsi-lateral neurological signs associated with lateralised Hansen type I disc extrusion. Of particular interest is an apparent predisposition in Irish wolfhound puppies (155). (2020) 256:9813. Vet J. Upchurch DA, Renberg WC, Turner HS, McLellan JG. (2016) 57:40915. Whilst the condition has been referred to as acute compressive HNPE to signify this compression (84), it is typically referred to by the shortened initialism of HNPE (Table 2). p. 101. These findings explain the extremely early chondroid metaplasia that occurs in chondrodystrophic breeds, but do not explain the single calcified disks that can be identified in large breed dogs (14, 15, 62, 118, 122). The surrounding annulus fibrosus on the other hand is composed of dense fibrous tissue with a complex lamellar structure, providing structural integrity as well as mobility (22). Konar M, Lang J, Fluhmann G, Forterre F. Ventral intraspinal cysts associated with the intervertebral disc: magnetic resonance imaging observations in seven dogs. doi: 10.2460/javma.249.7.767, 70. Jeffery ND, Mankin JM, Ito D, Boudreau CE, Kerwin SC, Levine JM, et al. Brisson BA, Holmberg DL, Parent J, Sears WC, Wick SE. Such advances also enhance our ability to classify IVDD for the purposes of diagnosis, prevention and treatment. Inter- and intraobserver agreement for diagnosing presumptive ischemic myelopathy and acute noncompressive nucleus pulposus extrusion in dogs using magnetic resonance imaging. Vet Radiol Ultrasound. Vet Rec. Intervertebral disc disease in dogs - part 2: comparison of clinical, magnetic resonance imaging, and histological findings in 74 surgically treated dogs. Packer RM, Hendricks A, Volk HA, Shihab NK, Burn CC. The imaging findings that can be used to make a diagnosis of ANNPE are listed below (18, 70, 139), with an example shown in Supplementary Figure 6: - Focal intramedullary T2-weighted hyperintensity of the spinal cord, - Spinal cord lesion located overlying an IVD, - Reduced volume of T2-weighted hyperintense nucleus pulposus signal in the affected IVD, - Mild narrowing of the affected IVD in mid-sagittal view. In the first histopathological descriptions of FCEM, the embolized material was examined closely using several histochemical stains leading to its identification as fibrocartilage (96, 103). Grunenfelder FI, Weishaupt D, Green R, Steffen F. Magnetic resonance imaging findings in spinal cord infarction in three small breed dogs. (1952) 121:36170. Vet Rec. Accuracy, intermethod agreement, and inter-reviewer agreement for use of magnetic resonance imaging and myelography in small-breed dogs with naturally occurring first-time intervertebral disk extrusion. Embryologically it derives from the mesoderm with the exception of the nucleus pulposus, which is a remnant of the notochord (104, 105). Spine J. (2001) 26:21128. Vet Clin North Am Small Anim Pract. (2012) 41:20714. Vet Radiol Ultrasound. The mass often appears like a worm extending along the spinal cord on the sagittal T2-weighted image and gives the appearance of a second spinal cord lying alongside or draped over and compressing the real spinal cord on transverse images. Brisson BA, Moffatt SL, Swayne SL, Parent JM. Whilst the clinical presentation may provide a high index of suspicion for a diagnosis of HNPE, differentials usually include IVD extrusion, ANNPE and fibrocartilaginous embolic myelopathy (FCEM). At that time Hansen described a case in which a single extreme violence has ruptured a disc that is not remarkably degenerated, and proposed the term traumatic disc prolapse (5). Olby NJ, MacKillop E, Cerda-Gonzalez S, Moore S, Munana KR, Grafinger M, et al. Vet Clin Pathol. A pathologic-anatomical interpretation of disc degeneration in dogs. Spinal cord infarction due to emboli arising from the intervertebral discs in the dog. They lie immediately adjacent to a rich vascular network from the epiphyseal arterial supply from which nutrients gain access to the IVD. doi: 10.1055/s-0038-1632970, 29. Tartarelli CL, Baroni M, Borghi M. Thoracolumbar disc extrusion associated with extensive epidural haemorrhage: a retrospective study of 23 dogs. Hansen HJ. 55. doi: 10.5326/0400316, 119. Building on these findings in the 1940s and 50s, Hansen and Olsson made huge advances in understanding the nature of canine IVDD, proposing a system of classification based on histopathological degenerative changes that persists today (2, 47). J Vet Intern Med. (2008) 162:47981. Whilst there are still many controversies in the categorization of types of disc-associated lesions in veterinary medicine, in this article we aim to review the relevant literature and to outline a consensus where possible. The resulting lesion is one of hemorrhagic ischemic necrosis of the spinal cord that tends to focus on the gray matter, frequently asymmetrically, reflecting the location of the emboli (96, 103). (2019) 56:895902. Magnetic resonance imaging of traumatic intervertebral disc extrusion in dogs. doi: 10.1111/j.1751-0813.2005.tb11620.x, 154. The concept of violent trauma (for example, vehicular trauma) causing a sudden rupture of the annulus fibrosus and subsequent extrusion of disc material into the vertebral canal, regardless of degenerative changes, was highlighted in dogs by Hansen in 1952 (5). 54. doi: 10.1016/j.cvsm.2010.05.003. J Am Anim Hosp Assoc. Vet Surg. Sanders SG, Bagley RS, Gavin PR. Vet Rec. - Small volume extradural material (T2-weighted hyperintense, T1-weighted hypointense) dorsal to the IVD with minimal to no spinal cord compression. J Small Anim Pract. Vet Pathol. Further investigations into outcome following surgical or non-surgical management of these rare cases are necessary, in which case accurate classification according to the presence of degenerative and non-degenerative IVD material may help to determine if subclassifying types of IIVDE is clinically useful. Practice patterns in the management of acute intervertebral disc herniation in dogs. Extended durotomy to treat severe spinal cord injury after acute thoracolumbar disc herniation in dogs. Increasingly, efforts have been made to adapt terminology used in the veterinary literature to include other recently described types of IVDD, as well as drawing from the human medical field with an emphasis on appropriate anatomical descriptions (10). Within the field of human neurology there are numerous examples of disorders that were classified based on histopathological and clinical findings that have been reclassified based on undercovering the genetic basis of the disease. Complete failure of this unit occurs with IVD herniation. De Decker S, Fenn J. The increasing understanding of the complex processes of IVD degeneration, and somewhat contradictory studies on the degree of degenerative changes occurring with types of IVD herniation such as ANNPE and HNPE makes classification based on degenerative processes less clear (9, 14, 81, 85). In his investigations into IVDD in dogs in the 1950s, Hansen found that dogs could be grouped according to the type of disc degeneration seen most frequently, into chondrodystrophic and non-chondrodystrophic dog breeds (5). Vet J. doi: 10.1016/j.tvjl.2013.04.003, 141. Liptak JM, Allan GS, Krockenberger MB, Davis PE, Malik R. Radiographic diagnosis: intramedullary extrusion of an intervertebral disc. (2013) 195:2929. (1951) 20:28093. Sometimes this hemorrhage can be dramatic and can cause multilevel spinal cord compression, and indeed appear as a hematoma (67, 68, 127, 128). Young to middle-aged chondrodystrophic dog breeds are most commonly affected by IVD extrusion, although as outlined above, they can also occur in non-chondrodystrophic dog breeds (62, 118, 122). It is likely that future IVDD classification systems will utilize further genetic findings, such as FGF4 genotype, to supersede traditional labeling of certain breeds as chondrodystrophic as a means of subcategorising affected dogs. Front Vet Sci. Royaux E, Martle V, Kromhout K, Van der Vekens E, Broeckx BJ, Van Ham L, et al. doi: 10.1111/j.1939-1676.2011.0739.x. 2. Although our understanding of the pathophysiology is incomplete, there is a broad consensus that it originates from the underlying intervertebral disc (79, 98, 103). (2001) 42:1418. Traumatic subarachnoid-pleural fistula in a dog. J Vet Intern Med. Vet Radiol Ultrasound. Kranenburg HJ, Grinwis GC, Bergknut N, Gahrmann N, Voorhout G, Hazewinkel HA, et al. doi: 10.1111/jsap.12496, 45. As an extension of this process, the nucleus pulposus becomes calcified and can be identified clearly on spinal radiographs. doi: 10.3109/17453675108991175, PubMed Abstract | CrossRef Full Text | Google Scholar, 5. J Small Anim Pract. DiVita MM, Bray KY, Williams LM, Traslavina RP. Human discal cysts are also typically associated with histological evidence of a well-defined cyst wall and the contents are of a serous or serosanguinous nature (135). doi: 10.1016/j.tvjl.2012.05.027, 13. Genetic discovery holds similar promise in furthering our understanding of canine IVD degeneration, as evidenced by the identification of the chromosome 12 FGF4 retrogene as a cause of chondrodystrophy and early, severe chondroid metaplasia with ensuing disc extrusion (1517). This limits the ability to perform high quality research or to accurately compare clinical data, as clinicians and researchers are restricted by the lack of clear disease definitions. Vet Rec. (1988) 29:61116. IIVDE is an uncommon diagnosis with the largest case series in veterinary literature consisting of 8 dogs, estimated to represent 0.5% of the surgical thoracolumbar IVD extrusion caseload in that study (89). Vet Radiol Ultrasound. (1974) 165:10804. doi: 10.1111/j.1740-8261.2007.00272.x, 133. Acta Vet Scand. Cardy TJ, De Decker S, Kenny PJ, Volk HA. As a result, the term ANNPE has become widely accepted in the veterinary literature as the most descriptive terminology for this condition and is therefore used here. J Vet Med Sci. J Am Vet Med Assoc. doi: 10.1016/j.tvjl.2016.08.012, 137. The previously documented association between IVD extrusion and body conformation in Dachshunds (120), likely reflects both the influence of the FGF4 retrogene and the importance of biomechanics in these breeds. Tidwell AS, Specht A, Blaeser L, Kent M. Magnetic resonance imaging features of extradural hematomas associated with intervertebral disc herniation in a dog. J Small Anim Pract. (1951) 8:195. Vet Comp Orthop Traumatol. Kitagawa M, Okada M, Kanayama K, Sakai T. Identification of ventrolateral intramedullary intervertebral disc herniation in a dog. Jensen VF. Acta Orthop Scand. J Vet Intern Med. Another possible approach is therefore to classify types of IVDD according to their typical clinical presentation. Spine. McConnell JF, Garosi LS. - Subtle reduction in volume of T2-weighted hyperintense nucleus pulposus signal in the disc caudal to the spinal cord lesion. Rupture of the dura mater in two dogs caused by the peracute extrusion of a cervical disc. doi: 10.1111/j.1748-5827.1999.tb03114.x, 58. Aust Vet J. Jeffery ND, Barker AK, Hu HZ, Alcott CJ, Kraus KH, Scanlin EM, et al. Since then, the term IVD extrusion has become more widely associated with the acute extrusion of nucleus pulposus from an IVD that has features of chondroid metaplasia, whilst IVD protrusion has largely been reserved chronic annulus fibrosus thickening originally associated with fibroid metaplasia. (1987) 23:373. (2013) 242:21722. A retrospective comparison of cervical intervertebral disk disease in nonchondrodystrophic large dogs versus small dogs. Cervical disc protrusions in the dog. Laminectomy for 34 dogs with thoracolumbar intervertebral disc disease and loss of deep pain perception. (2002) 43:15863. doi: 10.1111/j.1939-1676.2010.0613.x, 109. J Neuropathol Exp Neurol. 7. doi: 10.1038/gim.2013.28, 163. doi: 10.1111/j.1939-1676.1996.tb02056.x, 99. Feigin I, Popoff N, Adachi M. Fibrocartilagenous venous emboli to the spinal cord with necrotic myelopathy. Aikawa T, Fujita H, Kanazono S, Shibata M, Yoshigae Y. p. 2531. As the transitional zone blends into the annulus fibrosus the fibrous matrix becomes organized into a lamellar orientation. Thoracolumbar disc disease in large dogs: a study of 99 cases. (2015) 177:171. doi: 10.1136/vr.102988, Keywords: IVD, chondrodystrophy, degeneration, Hansen, extrusion, protrusion, Citation: Fenn J, Olby NJ and the Canine Spinal Cord Injury Consortium (CANSORT-SCI) (2020) Classification of Intervertebral Disc Disease. doi: 10.2460/javma.240.8.969, 126. We have aimed to provide a point of reference in matters of IVDD classification moving away from the restrictions of the traditional Hansen Type I and II system, as well as providing our interpretation of the meaning associated with terms currently used in the veterinary literature. Whilst both MRI and CT can be used to diagnose IVD extrusion, MRI has the benefit of allowing evaluation of soft tissues such as the spinal cord and intervertebral disks (39, 126). doi: 10.1016/S0195-5616(00)50004-7. Whilst there has been a gradual advancement in the terminology used in the veterinary literature to describe these additional types of IVDD, there remains great inconsistency. doi: 10.1016/j.tvjl.2012.10.011, 10. (2017) 19:41923. The authors encourage the consistent use of the terms used in the current series of papers clinically and when describing cases in the veterinary literature. Spine. 6. When using the term Hansen Type I IVD extrusion, we are referring to an acute extrusion of degenerative nucleus pulposus, with features of dehydration and cartilaginous calcification, whilst acknowledging that our current understanding of the underlying pathophysiology might be incomplete. Chick BF. Whilst extruded nucleus pulposus material remains in the extradural space in the case of IVD extrusion, HNPE and ANNPE, there have also been reports of nuclear material penetrating the dura mater (72, 88, 89, 91, 93, 101, 141, 142). Prognostic value of magnetic resonance imaging in dogs with paraplegia caused by thoracolumbar intervertebral disk extrusion: 77 cases (2000-2003). Batcher K, Dickinson P, Giuffrida M, Sturges B, Vernau K, Knipe M, et al. doi: 10.1159/000212177, 108. Indeed, Olsson stated as much in 1951, reporting that Disc protrusion [is] a synonym for disc herniation and disc prolapse (2). In some of these young dogs, onset appears to be associated with exercise or minor trauma. doi: 10.1053/jvet.2002.36015, 28. Falzone C. Canine acute cervical myelopathy: hydrated nucleus pulposus extrusion or intraspinal discal cysts? 114. J Hered. In the meantime, given the introduction of several new conditions related to the IVD to the veterinary literature in recent years, we have aimed to evaluate current systems of classification and terminology used to ensure consistent recording of IVDD types. Indeed, these dogs account for approximately half of all cases (79), and in some case series as many as 80% of dogs (99). However, by the same note it is important to consider that the treatment for all conditions with spinal cord compression is not necessarily the same. Clinical signs reflect the location of the extrusion along the vertebral canal and can range from mild discomfort with no neurological deficits to paralysis of the affected limbs with loss of pain perception. Intervertebral disc disease (IVDD) is a broad term that is widely used in veterinary medicine and encompasses a range of lesions affecting the intervertebral disc (Table 1). Indeed, the canine spinal cord is resistant to occlusion of single vessels due to its interconnected segmental arrangement and it has been suggested that FCEM will only result when multiple vessels are occluded simultaneously (96). doi: 10.1016/j.cvsm.2017.08.004, 134. The signalment and history of these dogs shows considerable overlap with dogs suffering from ANNPE, with distinguishing features including a slight breed predisposition (e.g., Border Collies more predisposed to ANNPE and Staffordshire Bull Terriers to FCEM) (69). Griffiths IR. As a result, although an ideal system of classification among types of IVDD does not currently exist, consistency across the veterinary literature in the terminology used for each individual form of IVDD would clearly be beneficial. Signs can be cervical or thoracolumbar, and age of onset ranges from 8 weeks to 14 years with males slightly more likely to be affected than females (79). (2007) 48:4247. In recent years further advances in the understanding of IVDD have been made, building on the seminal early work of Hansen and Olsson. Guevar J, Olby N. Minimally invasive microsurgical decompression of an intervertebral disc protrusion in a dog. Further details regarding diagnostic imaging in IVD protrusions can be found in the paper by Da Costa and others in this series. Vet Surg. Within the non-degenerate, normal IVD, the nucleus pulposus draws water down a strong osmotic gradient, creating an innately high intradiscal pressure (22). (2009) 234:495504. doi: 10.1111/j.1740-8261.2001.tb00917.x, 118. Can Vet J. Beltran E, Dennis R, Doyle V, de Stefani A, Holloway A, de Risio L. Clinical and magnetic resonance imaging features of canine compressive cervical myelopathy with suspected hydrated nucleus pulposus extrusion. None of the regions discussed thus far have a blood supply but there is light innervation of the outer annulus fibrosus (9, 104). Munana KR, Olby NJ, Sharp NJ, Skeen TM. The resulting biomechanical failure of the intervertebral disc unit is associated with fissuring of the annulus fibrosus and sclerosis of the endplates (5, 12, 110). The cutaneous trunci muscle reflex: a predictor of recovery in dogs with acute thoracolumbar myelopathies caused by intervertebral disc extrusions. Scott HW, McKee WM. This term refers to a subtype of acute herniation of a volume of partially or non-degenerate nucleus pulposus that results in a varying degree of extradural spinal cord compression (20). Traditionally this type of IVD herniation has been referred to as either Hansen Type II IVD disease, herniation or protrusion (Table 2).